Investigation of the WIMP annual modulation signature 291lower bound accounted for results achieved in accelerators. The calculations
have been performed according to the same astrophysical, nuclear and particle
physics considerations given in [7–9] and to the 90% C.L. recoil limit of [10]
(DAMA/NaI-0). Alternative analytical approaches, such as the one based on the
χtestvariable described in [8] and the Feldman and Cousins method [31], offer
substantially the same results.
Since the analysis of each data cycle independently [7–9, 13] gave consistent
results, a global analysis has been made properly including both the known
uncertainties on astrophysical local velocity,v 0 [21] and the constraint arising
from the upper limit on recoils measured in [10] (DAMA/NaI-0). According
to [21], the minimization procedure has been repeated by varyingv 0 from 170 to
270 km s−^1 to account for its present uncertainty; moreover, the case of possible
bulk halo rotation has also been analysed. The positions of the minima for
the log-likelihood function consequently vary [21]; for example, in this model
framework forv 0 = 170 km s−^1 the minimum is atMW = ( 72 +−^1815 )GeV
andξσp = ( 5. 7 ± 1. 1 )× 10 −^6 pb, while forv 0 = 220 km s−^1 it is at
MW=( 43 +− 912 )GeV andξσp=( 5. 4 ± 1. 0 )× 10 −^6 pb. The results obtained
in this model framework are summarized in figure 9.2, where the regions allowed
at 3σC.L. are shown:
(i) whenv 0 =220 km s−^1 (dotted contour);
(ii) when the uncertainty onv 0 is taken into account (continuous contour); and
(iii) when possible bulk halo rotation is considered (broken contour).The latter two calculations have been performed according to [21]. The
confidence levels quoted here have also been verified by suitable Monte Carlo
calculations; in particular, we note that the Feldman and Cousins analysis [31]
of the data gives quite similar results. These regions are well embedded in the
Minimal Supersymmetric Standard Model (MSSM) estimates for the neutralino
[32]. A quantitative comparison between the results from the model-independent
and model-dependent analyses has been discussed in [9].
Finally, many assumptions on the nuclear and particle physics used in these
calculation (as well as in those of exclusion plots) are affected by uncertainties,
which—when taken into account—would enlarge the regions of figure 9.2 and, as
mentioned, consequently vary the positions of the minima for the log-likelihood
function. For example, as in [9] we mention the case of the iodine form factor,
which depends on the nuclear radius and on the thickness parameter of the nuclear
surface; it has been verified that, varying their values with respect to those used in
the analysis in [9] by 20%, the locations of the minima will move toward slightly
largerMWand toward lowerξσpvalues, while the calculated 2–6 keVSmvalues
will increase by about 15%.